Holland J Nathaniel, DeAngelis Donald L
Department of Biology, University of Miami, P.O. Box 249118, 33124, Coral Gables, FL, USA.
U.S. Geological Survey/Biological Resources Division, Department of Biology, University of Miami, P.O. Box 249118, 33124, Coral Gables, FL, USA.
Oecologia. 2001 Feb;126(4):575-586. doi: 10.1007/s004420000542. Epub 2001 Feb 1.
Mutualistic interactions almost always produce both costs and benefits for each of the interacting species. It is the difference between gross benefits and costs that determines the net benefit and the per-capita effect on each of the interacting populations. For example, the net benefit of obligate pollinators, such as yucca and senita moths, to plants is determined by the difference between the number of ovules fertilized from moth pollination and the number of ovules eaten by the pollinator's larvae. It is clear that if pollinator populations are large, then, because many eggs are laid, costs to plants are large, whereas, if pollinator populations are small, gross benefits are low due to lack of pollination. Even though the size and dynamics of the pollinator population are likely to be crucial, their importance has been neglected in the investigation of mechanisms, such as selective fruit abortion, that can limit costs and increase net benefits. Here, we suggest that both the population size and dynamics of pollinators are important in determining the net benefits to plants, and that fruit abortion can significantly affect these. We develop a model of mutualism between populations of plants and their pollinating seed-predators to explore the ecological consequences of fruit abortion on pollinator population dynamics and the net effect on plants. We demonstrate that the benefit to a plant population is unimodal as a function of pollinator abundance, relative to the abundance of flowers. Both selective abortion of fruit with eggs and random abortion of fruit, without reference to whether they have eggs or not, can limit pollinator population size. This can increase the net benefits to the plant population by limiting the number of eggs laid, if the pollination rate remains high. However, fruit abortion can possibly destabilize the pollinator population, with negative consequences for the plant population.
互利共生的相互作用几乎总是给每个参与相互作用的物种带来成本和收益。总收益与成本之间的差异决定了净收益以及对每个参与相互作用的种群的人均影响。例如，专性传粉者（如丝兰蛾和塞尼塔蛾）对植物的净收益取决于蛾传粉使胚珠受精的数量与传粉者幼虫吃掉的胚珠数量之间的差异。显然，如果传粉者种群数量庞大，那么由于产卵数量众多，植物的成本就很高；而如果传粉者种群数量很小，由于缺乏授粉，总收益就很低。尽管传粉者种群的规模和动态可能至关重要，但在研究诸如选择性落果等可以限制成本并增加净收益的机制时，它们的重要性却被忽视了。在这里，我们认为传粉者的种群规模和动态在决定植物的净收益方面都很重要，而且落果会对这些产生显著影响。我们构建了一个植物种群与其传粉种子捕食者之间的互利共生模型，以探讨落果对传粉者种群动态的生态后果以及对植物的净影响。我们证明，相对于花朵数量，植物种群的收益随传粉者丰度呈单峰变化。无论是有卵果实的选择性落果还是不考虑是否有卵的随机落果，都可以限制传粉者种群规模。如果授粉率仍然很高，这可以通过限制产卵数量来增加植物种群的净收益。然而，落果可能会使传粉者种群不稳定，对植物种群产生负面影响。
